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Industrial grease traps

A food factory on the outskirts of Cape Town that produces packet soups and frozen convenience meals was experiencing sewer blockages and bad odours in their dispatch yard

When the factory was originally built, the plumber had installed two 1,000lt underground tanks as 'interceptors'. During recent years, production has increased threefold and the firm has expanded into more space in the building. Local neighbours complained about the bad smells and the municipality continuously cleared blockages from the 150mm outfall sewer – greasy food sludge and fat deposits were found up to 1.5km down-line.


CH: Industrial grease traps - blocked interceptor  Blocked interceptor


The factory spent some R12k per month on a waste removal company that was contracted to 'suck out' the tanks when necessary – a time-consuming task in the congested service yard where delivery trucks were frequently parking on the inspection covers. The factory contracted a cleaning firm that came in after the last shift at 10pm to wash the floors and restrooms. Chosen for their rates, the cleaning firm used cheap detergents and chlorine based disinfecting compounds to sterilize the drains and interceptors.

Eventually, after a spate of blockages, BIO-SYSTEMS SA caught wind of their dilemma and approached the factory. We produced a costing schedule designed to show the directors of their parent company (who operated 1,800 km away in Johannesburg and rarely visited the plant) that they could save money by using our services.

However, there was a hurdle: in order to do this, the company had to allocate funds to modify their drainage system. Months went by and they paid the municipal surcharge because it was cheaper than investing more capital. Eventually, the parent company was 'shamed' into compliance because their principal customer had to comply with ISO14000 to maintain their export market.

At last! We were called in and asked to produce a 'plan'. Here's how we tackled the problem:

  • The production was in two wings of the same building, like a letter ’H’ on plan, with staff parking in the front and the service yard at the back with a wing either side. One wing was dedicated to soups and the other for prepared meals and fancies.
  • We rearranged the drain lines so each wing discharged to a 8m3 waste sump with an overflow (in case of electrical failure) to the existing u/g 1,000lt tanks, which we pumped out and bioremediated.
  • Floor drains were already in place, but we installed three RGT500 Under Sink Particle Interceptors beneath the prep bowls in the prepared meal wing. Each sump was fitted with a 'grinder' pump (we used stainless steel units to withstand the alternating caustic and acid conditions experienced during the kettle scalding cycles). Fitted with float switches and a 40mm AirMix Injector on the delivery side, they were timed to intermittently circulate/agitate/aerate their effluent between delivery cycles.
  • Both pumps delivered to a RGT2000 grease trap (seen here, ready for installation) mounted on the floor beneath a shade fly roof in the screened-off solid waste area. This stainless steel unit is fitted with twin sludge baskets and rated at 11lt per second. It has a scouring valve and an oil take-off tap in the stilling tank. With the bulkhead rim 1.2m above ground level, it is easy to maintain and clean. The section on which we mounted the unit was bunded and epoxy painted to our direction – a boon if it should overflow (bunding is also a requirement of the OSSHA act).

   CH: industrial grease traps - RGT2000 grease trap

RGT 2000 grease trap ready for installation

  • The outflow, displaced by gravity, ran into a DAF unit, which was a fabricated 'SS' tank 6m long x 2m wide x 900mm deep with a perforated manifold in the floor. Divided into three by 150mm deep under-pass baffles, it allowed the strained effluent to slow and for emulsified fats to be bubbled to the surface by the mist of ultra fine air emanating from the manifold, which was fed with circulating effluent passing through a second 40mm AirMix Injector. 
  • All sinks and floor drains were dosed with BIO-SYSTEMS L2120 once a day, as prescribed, and each sump received 125g BIO-SYSTEMS B220 every week (on Monday mornings). We have made provision for a rotary screen on each line before the sumps, but they have not proven necessary to date. However, if the nature of production changes in future, they may be required.

Other modifications

The other major modification was to the chemical usage. The cleaning contractor was replaced by another firm that now uses our BIO-SYSTEMS HSDG to wash the floors each night. This has made a considerable difference as the floors are now totally non slip and the organic loading on the system has been reduced – HSDG is an encapsulant that removes floor sourced COD from the pollution equation.

Final effluent quality to sewer has improved dramatically and the pollution inspector is returning values of COD consistently less than 1,500pm, whereas 8,000-21,000ppm were common before. Running costs are down too. Our monthly fee to manage the system is R5,500 per month plus R475 per month for the supply of HSDG to the cleaning contractor. The factory no longer pays a financial penalty to the municipality, which used to be in the region of R12k per month. The factory’s extra cost is now R6k against a previous cost of R24k, indicating a saving on production of R18k per month. Considering that the modifications cost around R110k, that's a payback of around six months!

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